Put npm-debug.log file in a consistent place

lib/utils/error-handler.js

@@ -9,7 +9,12 @@ var cbCalled = false
   , path = require("path")
   , wroteLogFile = false
   , exitCode = 0
+  , debugFile
 
+function getDebugFile() {
+  if (debugFile) return debugFile
+  return debugFile = path.resolve(npm.cache, "npm-debug.log")
+}
 
 process.on("exit", function (code) {
   // console.error("exit", code)
@@ -24,7 +29,7 @@ process.on("exit", function (code) {
     if (wroteLogFile) {
       log.error("", [""
                 ,"Additional logging details can be found in:"
-                ,"    " + path.resolve("npm-debug.log")
+                ,"    " + getDebugFile()
                 ].join("\n"))
       wroteLogFile = false
     }
@@ -51,7 +56,7 @@ function exit (code, noLog) {
   if (log.level === "silent") noLog = true
 
   if (code && !noLog) writeLogFile(reallyExit)
-  else rm("npm-debug.log", function () { rm(npm.tmp, reallyExit) })
+  else rm(getDebugFile(), function () { rm(npm.tmp, reallyExit) })
 
   function reallyExit() {
     // truncate once it's been written.
@@ -322,7 +327,7 @@ function writeLogFile (cb) {
   wroteLogFile = true
 
   var fs = require("graceful-fs")
-    , fstr = fs.createWriteStream("npm-debug.log")
+    , fstr = fs.createWriteStream(getDebugFile())
     , util = require("util")
     , os = require("os")
     , out = ""